1. Field of the Invention
The present invention relates to a laser beam processing apparatus that executes laser beam processing using a fiber laser beam.
2. Description of the Related Art
Conventionally, a laser having an optical-fiber structure is known that oscillates and outputs a raw laser beam having a predetermined wavelength by optically pumping a core thereof including a luminous element using an excitation beam, so called a “fiber laser”. Because the fiber laser uses a very elongated core as the active medium thereof, the fiber laser can oscillate and output a laser beam having a small beam diameter and a small beam divergence angle (a fiber laser beam). In addition, the excitation beam injected into the fiber consumes completely the excitation energy thereof by crossing many times the core while the ray propagates on a long optical path and, therefore, a fiber laser beam can be created at a very high oscillation efficiency. In addition, for the fiber laser, the beam mode of the fiber laser beam is very stable because the core of the fiber generates no thermal lens effect.
The conventional fiber laser beam processing apparatus sets an electric current value for excitation corresponding to a desired laser output, and a laser power source supplies an excitation current corresponding to the current value having been set to an excitation light source such as, for example, a laser diode (LD). Because the length of the fiber for the fiber laser can arbitrarily be selected, an output end terminal of the fiber laser is brought to a processing site and a fiber laser beam oscillated and outputted from the fiber laser is directly applied to a processing point on a work to be processed through a condensing optical system.
However, the conventional fiber laser beam processing apparatus has an aspect of unstable laser output thereof due to an influence of degradation of the excitation LD, a wavelength shift, etc. Therefore, the reproducibility and the reliability of the laser beam processing are poor. Because the fiber laser is also vulnerable to influences of the heat, vibrations, ambient light, etc., problems have also arisen that the fiber laser tend to occur degradation of the laser oscillation performance, damage, degradation, etc., of components thereof (the optical fiber for oscillation, optical resonator, etc.).